Diffusion transfer process



July 20, 1965 w RYAN 3,196,015

DIFFUSION TRANSFER PROCESS Filed Jan. 31, 1962 SPREADER SHEET PROCESSINGOOMPOSIT ION PHOTOSENSITIVE LAYER IMAGE- RECEIVING LAYER SUPPORT FIGQISUPPORT PHOTOSENSITIVE LAYER PROCESSING COMPOSITION IMAGE RECEIVINGELEMENT F-IG.2

TRANSPARANT SUPPORT (DLOR SCREEN ELEMENT IMAGE-RECEIVING LAYERPHOTOSENSITIVE LAYER FIG.3

SUPPORT LAYER CONTAINING IMAGE -FURMING COMPONENTS PHOTOSENSITIVE LAYERE CONTAINER IMAGE RECEIVING LAYER FIG.4

INVENT R.

BY MW ATTORNEYS United States Patent 3,196,015 DH FUSIQN TRANSFERPRGCESS Wiiiiam H. Ryan, Carlisle, Mass, assignor to PoiaroidCorporation, Cambridge, Mass, a corporation of Deiaware Filed Jan. 31,1962., Ser. No. 170,(lt 8 3 Claims. (ct. 9s-2e;

This invent-ion relates to photography and, more particularly, to novelphotosensitive photographic elements.

It is one object or the present invention to provide novelphotosensitive emulsions.

Another object of the present invention is to provide methods offabricating same.

A further object of the present invention is to provide certain novelsilver halide emulsions wherein photosensitive silver halide crystal-sare disposed in specified synthetic polymeric binder-s.

A still further object of the present invention is to provide specifiedphotosensitive silver halide emulsions for employment in d'ifiusiontransfer photographic processes.

Other objects of the present invention will in part be obvious and willin part appear hereinafter.

The invention accordingly comprises the several steps and the relationand order of one or more of such steps with respect to each of theothers, and the product possessing the features, properties and therelation of elements which are exemplified in the following detaileddisclosure, and the scope of the application of which will be indicatedin the claims.

For a fuller understanding of the nature and objects of the inst-antinvention, reference should be had to the following detailed descriptiontaken in connection with the accompanying drawing wherein:

FIGURE 1 is a diagrammatic enlarged cross-sectional view illustratingthe association of elements during one stage of the performance of atransfer process, for the production of silver prints, and showing, asone of the elements, embodiment of the novel photosensitive emulsions ofthe present invention, the thicknesses of the various materials beingexaggerated;

FIG. 2 is a View similar to that of FIGURE 1 illustrating theassociation of elements during one stage of the performance of anotherdiffusion-transfer process, for the production of silver prints, whichillustrates another embodiment of novel photosensitive elements of thepresent invention;

FIG. 3 is a diagrammatic enlarged cross-sectional view of one embodimentof the novel photosensitive element of the present invention, for use inobtaining additive multicolor images, comprising a support, an additivemulticolor screen element, an embodiment of the present invention as thephotosensitive emulsion, and an image-receiving stratum; and

FIG. 4 is a diagrammatic enlarged cross-sectional view of one embodimentof the novel photosensitive element of the present invention, for use inobtaining subtractive color images, comprising a photosensitive elementwhich itself comprises a support, a layer containing color imageformingcomponents and an embodiment of the present invention as thephotosensitive emulsion; a rupturable container; and an image-receivingelement.

The present invention comprehends improved photosensitive silver halideemulsions, comprising in whole or in part the specified syntheticbinders detailed hereinafter, which find especially advantageousutilization in dilfusiont-ransfer processes.

In photographic diffusion-transfer processes, an exposed photosensitivesilver halide emulsion is developed and, substantially concurrentlytherewith, soluble imageforming components are obtained according to thepointto-point degree of exposure of the emulsion. These solubleimage-forming components are transferrd, in solution, from the emulsionto a suitable print-receiving layer to provide thereto the desired imageformation.

In dilTusion transfer processes, for the formation of silver images, alatent image contained in an exposed photosensitive silver halideemulsion is developed and, almost concurrently therewith, a solublesilver complex is obtained by the action of a silver halide solvent uponundeveloped silver halide of said emulsions. Accordin to one mechanism,the photosensitive silver halide emulsion is developed with a processingcomposition in a viscous condition which is spread between thephotosensitive elements comprising 'the silver halide emulsion and animage-receiving element comprising a suitable silver precipitatinglayer. The processing composition effects development of the latentimage in the emulsion and, substantially contemporaneous therewith, forma soluble silver complex, for example, a thiosulfate or thiocyanatecomplex, with undeveloped silver halide. This soluble silver complex is,at least in part, transported in the direction of the image-receivingelement and the silver thereof is large precipitated in the silverprecipitating layer of the element to form an image therein.

Additive color reproduction may be produced by exposing a photosensitivesilver halide emulsion through an additive color screen having filtermedia or screen elements each of an individual additive color such asred or blue or green, and by viewing the reversed or positive silverimage, formed by transfer to a transparent imagereceiving element,through the same or a similar screen which is suitably registered withthe positive image carried by the image-receiving layer.

United States Patent No. 2,983,606, issued May 9, 1961, discloses andclaims diffusion transfer processes wherein initially mobile anddilfusible dye developers, that is, complete dyes which contain in thesame molecular structure a silver halide developing function, areutilized in the development of an exposed photosensitive silver halideemulsion, effecting thereby immobilization of the dye developers in thephotosensitive emulsion, as a function of the point-'to-point degree ofexposure thereof, and transferring, at least in part, the resultantimagewise distribution of mobile dye developer from unexposed areas ofthe photosensitive emulsion, by imbibition, to a superposedimage-receiving layer or element, to impart thereto a subtractive-colortransfer image.

United States Patents Nos. 2,647,049, issued July 28, 1953; 2,661,293,issued December 1, 1953; 2,698,244, issued December 28, 1954; 2,698,798,issued January 4, 1955; and 2,802,735, issued August 13, 1957, disclosediffusion transfer processes wherein color coupling techniques areutilized to provide subtractive color images. Image-forming componentscomprising one or more color developing agents and one or more colorformers or couplers are reacted to provide color image formation to asuperposed image-receiving element.

It has now been discovered that photosensitive silver halide emulsionscomprising hydroxyethyl polyvinyl alcohol, as the colloid binder, areespecially useful for diffusion transfer processes.

The novel photosensitive emulsions of the instant invention may beprepared by reacting a water-soluble silver salt, such as silvernitrate, with at least one water-soluble halide, such as potassium orsodium bromide, preferably together with potassium or sodium iodide, inan aqueous solution of a gelatin colloid peptizing agent. The dispersionof silver halide thus formed contains Watersoluble salts, as a byproduct of the double decomposition reaction, in addition to anunreacted excess of either of the initial salts. To remove this solublematerial, the gelatin dispersion has generally been set by means ofchilling, the so-set dispersion noodled, and the noodles then washedwith cold water.

Alternative procedures comprise coagulating the gelatin, separating thecoagulum from the supernatant liquor, and washing the separated coagulumwith water.

The fact that certain specified derivatives may be prepared fromgelatin, employed as the peptizer for preparing dispersions of silverhalide, and that the resultant dispersion of silver halide, in thosederivatives, is acidcoagulable and will form silver halide gelatinderivative granules, when the dispersion is adjusted to the proper 'pH,is disclosed in US. Patents Nos. 2,481,650, issued September 13, 1949;2,614,928, issued October 21, 1952; 2,614,929, issued October 21, 1952;2,728,662, issued December 27, 1955; and 2,956,880, issued October 18,1960.

The coagulation of silver halide gelatin dispersions by theincorporation of specified additives is disclosed in US. Patents Nos.1,844,716, issued February 9, 1932 (the salt forming elements of GroupIV of the Periodic Table); 2,489,341, issued November 29, 1949 (anionsoaps); 2,527,261, issued October 24, 1950 (anion soaps); 2,527,268,issued October 24, 1950 (anion soaps); and 2,618,556, issued November18, 1952 (ammonium salts, salts of the alkali metals having an atomicweight less than 140, and salts of the metals of Group II of thePeriodic Table having an atomic weight less than 140).

The coagulation of the aforementioned silver halide gelatin derivativedispersions of US. Patent No. 2,614,- 929, by the addition of thewater-soluble salts of cadmium, zinc, aluminum, iron, nickel, chromium,and lanthanum, is disclosed in U.S. Patent No. 2,768,079, issued October23, 1956.

The incorporation of the silver halide crystals in gelatin, as thepeptizing agent, has had extensive utilization because of the manydesirable properties of gelatin not possessed by known syntheticpolymers. This is true especially of gelatins eifects on silver halidegrains and its influence on the crystal growth of the silver halides.

The coagulum or noodles which have been washed by either of the twogeneral methods outlined above may be redissolved and used in formingsilver halide-hydroxyethyl polyvinyl alcohol photographic emulsions byredispersing the silver halide-gelatin mixture in water and adding asolution of hydroxyethyl polyvinyl alcohol to the redispersed grains.

The emulsions so prepared readily respond to the standard methods ofchemical and optical sensitization. However, it should be noted that,where desired, sensitization may be carried out on the redispersedsilver halide prior to the addition of the hydroxyethyl polyvinylalcohol.

Where desired, photosensitive silver halide crystals may be formed, forexample, by vacuum deposition techniques, without the necessity ofemploying a dispersion medium during crystal formation, such as thepreviously described gelatin, and thereafter directly dispersed in thehydroxyethyl polyvinyl alcohol polymeric binder. Silver halide crystalsmay also be directly deposited or formed on hydroxyethyl polyvinylalcohol by vacuum deposition techniques. For example, the silver halidecrystals may be formed on flake hydroxyethyl polyvinyl alcohol,

' which may be dissolved in water or aqueous alcohol for coatingoperations, or the silver halide crystals may be formed on the surfaceof a'continuous hydroxyethyl polyvinyl alcohol web which web, ifdesired, may be granulated and dissolved for subsequent coating oremployed as formulated.

In addition, the photosensitive silver halide crystals may be formeddirectly in hydroxyethyl polyvinyl alcohol. In this method, the silverhalide crystals are formed by reacting a Water-soluble silver salt withat least one Water-soluble halide in an aqueous solution of hydroxyethylpolyvinyl alcohol. The previously identified water-soluble by-products,formed during reaction, may be removed by coagulating the silver halidehydroxyethyl polyvinyl alcohol dispersion by means of acetone,concentrated sodium sulfate solutions, or any of other known coagulatingagents for hydrophilic synthetic hydroxyl polymers, and Washing thecoagulated dispersion to eifect removal of the impurities. The coagulatemay then be redissolved by the addition of water or aqueous alcoholsolutions, sensitized, the desired additives incorporated therein, andcoated according to procedures known in the art. In the alternative, thesilver halide hydroxyethyl polyvinyl alcohol dispersion may also havethe aforementioned water-soluble by-products removed by dialysistechniques or by contact of the dispersion with ion exchange resins andthe like.

Although the light-sensitive material of a photographic emulsion isgenerally a compound of silver, for example, one or more of the silverhalides, of which silver chloride, silver bromide and silver iodide areexamples, it will be recognized that compounds of iron, chromium, andselected other metals, as well as certain organic compounds, forexample, diazonium compounds, may be substituted for the aforementionedsilver halide in the emulsions of the present invention. A preferredsilver halide emulsion comprises a silver iodobromide emulsion.

The resultant emulsion of the resent invention may be sensitized, thedesired additives incorporated therein,

ventional procedures known in the emulsion manufacturing art.

The emulsions of this invention may be coated onto various types ofrigid or flexible supports, for example, glass, paper, metal, polymericfilms of both the synthetic types and those derived from naturallyoccurring products, etc. The specially suitable material includes paper;aluminums; polymethacryl-ic acid, methyl and ethyl esters; vinylchloride polymers; polyvinyl acetal; polyamides such as nylon;polyesters such as polymeric films derived from ethyleneglycol-terephthalic acid; and cellulose derivatives such as celluloseacetate, triacetate, nitrate, propionate, butyrate, acetate-propionate,or acetatebutyrate.

As previously mentioned, the preferred light-sensitive material of theinstant photographic emulsions comprises a compound of silver, forexample, one or more of the silver halides of which silver chloride,silver bromide and silver iodide are examples. It will be understoodthat silver halides of varying halide concentrations may beadvantageously employed.

The emulsions of the present invention may be chemically sensitized byany of the accepted procedures. For example, the emulsions may bechemically sensitized with sulfur compounds such as sodium thiosulfateor thiourea; with reducing substances such as stannous chloride; withsalts of noble metals such as gold, rhodium and platinum; with aminesand polyamines; with quaternary ammonium compounds such as a-picoliniumbromide, etc; and with polyethelene glycols and derivatives of same.

'The emulsions may also be optically sensitized with cyanine andmerocyanine dyes as described in US. Patent Nos. 1,846,301; 1,846,302;1,942,854; 1,990,507; 2,112,- 2,165,338; 2,493,747; 2,493,748;2,503,776; 2,519,- 001; 2,666,761; 2,734,900; 2,739,964; etc.

Where desired, suitable anti-foggants, restrainers, accelerators,preservatives, coating aids, and/or stabilizers may be included in thecomposition of the emulsion.

The hydroxyethyl polyvinyl alcohol which is employed as the vehicle inthe herein described photographic emulsions may comprise either a highviscosity, medium viscosity or low viscosity type.

As is well known, polyvinyl alcohol is obtained commerc1ally byhydrolyzing polyvinyl acetate whereby substantially all of the acetategroups are converted to hydroxyl groups, depending on the method ofmanufacture The present invention includes the use of hydrolyzedpolyvinyl acetates of which the major proportion of the resultingmaterial is polyvinyl alcohol, most preferably those having a polyvinylalcohol content of 75% or more. The invention also includes within itsscope the use of any of the far hydrolyzed polyvinyl acetates (and farpropionates and far butyrates, etc.) as vehicles in the preparation ofthe instant photographic emulsions.

These polymers contain suflicient aliphatic hydroxyl groups orintralinear vinyl alcohol units to make them hydrophilic or soluble incold and hot water.

One method of preparing the hydroxyethyl substituted polyvinyl alcoholpolymers employed in the present invention is to react an aqueoussolution of polyvinyl alcohol with liquid ethylene oxide at elevatedtemperatures in a pressure vehicle. The liquid ethylene oxide preferablyis in excess of that which is to participate in the reaction. Althoughthe reaction conditions may be vared within wide limits, preferaby thereaction temperature ranges from about 60 to 100 C., and the reactionduration ranges from about to 50 hours. The number of hydroxyethylsubstituents can be controlled by limiting the reaction temperature andvarying the reaction duration.

The reaction itself may be catalyzed by a base, such as an alkali metalhydroxide or a tertiary amine. For example, immediately precedingreaction, the polyvinyl alcohol may be contacted with the base.

The preferred hydroxyethyl polyvinyl alcohol polymers employed in thepresent invention contain from 17 to combined ethylene oxide by weight.The resultant polymers, hydrophilic in character, possess greatflexibility and a high degree of moisture permeability.

- It will be recognized that hydroxyethyl polyvinyl alcohol having moreor less combined ethylene oxide by weight than the preferred rangedelineated may also be employed. Generally, where the combined ethyleneoxide is within the range of about 25 to by weight,

the polymer possesses rubber-like properties. Where the combinedethylene oxide is in excess of about 35% by weight, the polymerpossesses gum properties. However, all are completely and readilysoluble in water.

The term hydroxyethyl polyvinyl alcohol is employed throughout theinstant specification to designate the reaction product of polyvinylalcohol and ethylene oxide. It is generally believed that the reactionproduct comprises polyvinyl alcohols containing recurring groupsrepresented by the general formula:

The novel hydroxethyl polyvinyl alcohol of the instant invention will beillustrated in greater detail in conjunction with the following specificexample which sets out a representative preparation of the novelemulsions, which, however, is not limited to the detailed descriptiontherein set forth and is intended to be illustrative only.

A phthalic anhydride derivative of gelatin was prepared by dissolving100 grams of gelatin in 1100 cc. of water at a temperature of C. The pHof the resultant solution was adjusted, to within the range of 9.5 to10.5, with aqueous 10% sodium hydroxide solution. 11 grams of phthalicanhydride, dissolved in 77 cc. of dry acetone, was then added graduallyover a 30-minute period, during which addition the solution pH wasmaintained within the previously denoted range by the addition ofaqueous 10% sodium hydroxide solution. The reaction was continued for 30minutes, at a temperature of 40 C after which time the pH was lowered towithin the range of 6 to 7, with an aqueous 10% sulfuric acid solution.The mixture was then chilled and set.

A silver halide gelatin derivative dispersion was prepared byformulating a solution comprising 226 grams of the last-preparedmixture, 161 grams of potassium bromide, 8 grams of potassium iodide,and 1250 cc. of distilled water. To this solution, maintained at atemperature of about C., was added a solution comprising 200 grams ofsilver nitrate dissolved in 1600 cc. of water.

The dispersion was cooled to approximately 10 C., with stirring, andthen adjusted to a pH of about 3.0, with sulfuric acid. The resultantprecipitate was separated from the mother liquor and washed with chilleddistilled water.

56 grams of the washed precipitate was then added to a hydroxyethylpolyvinyl alcohol containing solution comprising 10 grams ofhydroxyethyl polyvinyl alcohol dissolved in 50 cc. distilled water. ThepH of the mixture was then adjusted to about 5.7 with an aqueous 10%sodium hydroxide solution. 0.8 mg. of sodium thiosulfate was then addedto the resultant emulsion, which was then ripened at approximately 52 C.for about 2 hours.

The emulsion contained 13.8 weight percent silver, 8.6 weight percenthydroxyethyl polyvinyl alcohol and 1.9 weight percent gelatin.

The hydroxyethyl polyvinyl alcohol emulsions of the present inventionpossess unexpected advantages over those possessed by prior artemulsions containing conventional polyvinyl alcohol colloid binders. Asan example of such advantages, in diffusion-transfer processesdistinctly increased process speed has been achieved.

To illustrate the unexpected advantages achieved by reason of theinstant invention, three separate photosensitive silver halide emulsionswere fabricated in accordance with the following procedure. An emulsion,designated hereinafter as Emulsion A, was prepared in accordance withthe previously detailed description. A second emulsion, designatedhereinafter as Emulsion B, was formulated as in accordance with thepreviously detailed procedure, except that the addition of sodiumthiosulfate, a sensitizing agent, was deleted from the formulation. Athird emulsion, designated hereinafter as Emulsion C, was formulated inaccordance with the previously described procedure with the exceptionthat Elvanol 74-05 (trade name of E. I. du Pont de Nemours, Inc.,Wilmington, Delaware, for polyvinyl alcohol) was substituted in thedetailed formulation for the instant hydroxyethyl polyvinyl alcohol.

Each emulsion was coated on cellulose triacetate film base, dried andexposed in a sensitometer. Each photoexposed emulsion was then transferprocessed by superposition of the exposed emulsion on a receiving sheetsuch as the commercial image-receiving sheet, a component of PolaroidLand Picture Roll Type 42 (Polaroid Corporation, Cambridge,Massachusetts), and distributing a transfer processing composition, byrupture of a frangible container holding same between the emulsion andthe imagereceiving element and provided the results detailedhereinafter.

Positive transfer print characteristics density in the resultantpositive.

Difiusion Emulsion Transfer Slope Density Minimum Exposure Range DensityIndex The Diffusion Transfer Exposure Index is based on a curve relatingoriginal exposure of the emulsion to the It has been foundexperimentally that the Diffusion Transfer Exposure Index of a silvertransfer process may be determined by plot-ting a characteristic curveof the reflection density of the positive as a function of the logexposure of the negative, determining the exposure in meter-candleseconds (m.c.s.) at the point on this curve corresponding to a densityof 0.50, and dividing the constant, 4.0, by the exposure so determined.The exposure index thus obtained indicates generally the correctexposure rating of a silver transfer process to which an exposure meter,calibrated to the ASA Exposure Index, must be set in order that it givecorrect exposure data for producting transfer prints of satisfactoryhigh quality. The aforementioned slope refers to the slope of thelast-mentioned characteristic curve.

'As may be observed, the exposure index of the hydroxyethyl polyvinylalcohol emulsions of the instant invention, prepared in the same manneras conventional polyvinyl alcohol emulsions, is substantially greater,when processed in diffusion-transfer processes providing approximatelyequal maximum densities. While the reason for this increased exposureindex is not definitely known, it may be possible that the matrixmolecules may confer a sensitizing effect; however, it should also benoted that the hyd-roxyethyl polyvinyl alcohol emulsions possess agreater slope and a lower minimum density than that obtained whenconventional polyvinyl alcohol emulsions are employed.

While in the prior art it has generally been necessary that photographicemulsion layers possess the dimensional stability to withstand extensivecontact with developer,

fixer and washing solutions, the diffusion transfer processes hereindetailed require no long term physical stability of the emulsion layer.Inasmuch as development and transfer may be effected in less than aminute, preferably in a fraction of a second to seconds, it is possiblefor the emulsion layer itself to melt or dissolve completely in theprocessing fluid without any substantial detriment to the transfer imagefunction. In fact, the ready solubility of the emulsion may actuallyassist materially in causing the transfer of image-forming components totake place in a shorter time interval than that obtainable whenconventional materials are employed. In general, during transferprocessing, any liquified emulsion is held in position betweensupporting layers, such that transfer formation is generally consideredsubstantially completed prior to sufficient lateral diffusion to affecttransfer image formation.

For these reasons an emulsion in which the colloid binder compriseswater-soluble hydroxyethyl polyvinyl alcohol is uniquely adapted toemployment in the transfer processes hereinafter explicitly detailed.

Particularly desirable image-receiving elements for use in silverdiffusion transfer processes are specifically set forth in US. PatentNo. 2,647,056, issued July 28, 1953, and US. Patent No. 2,698,237,issued December 28, 1954.

Examples of diffusion transfer processing composition formulations areset forth in the aforementioned U.S. Patent No. 2,647,056.

For carrying out the process of the invention wherein there is formed apositive image of the subject matter of a latent im-age contained in aphotosensitive silver halide emulsion or the like, a preferred form ofthe processing agent comprises a Water solution of a developer, analkali for imparting to the solution a sufficiently high alkalinity topermit the developer to carry out its developing function, a substancefor forming :a soluble complex with silver halide, and a film-formingmaterial. The developer in the agent acts to develop any latent image inthe emulsion and the silver halide solvent forms a soluble complex withthe relatively unexposed silver halide during the development, whichcomplex may be transported from the emulsion to another stratum ofmaterial of the lamination to form in said other stratum a positiveimage comprising silver. The film-forming material, which is preferablya high molecular weight polymer, imparts to the 0 composition apredetermined high viscosity and is of such character as to retain itsviscosity-imparting and filmforming properties in an aqueous alkalinesolution so that the processing agent, once its ingredients have beenmixed and have attained an equilibrium, remains uniformly viscous forany given temperature for long periods of time.

The film-forming material in the foregoing alkaline composition ispreferably one of the class of high molecular weight polymers whichinclude in their chemical structure such groups as, for example, theether, alkyl, hydroxyl, carboxyl and acetyl groups that are stable toalkalies and which contain none of the chemical groups, such as theester and acid chloride groups, that are unstable to alkal'ies. Thepolymers also contain groups such as the hydroxyl and/or carboxyl groupswhich tend to solubilize in aqueous alkaline solutions. Suitableexamples of such polymers are the alkali-inert and watersoluble celluosederivatives such as sodium carboxymethyl cellulose and hydroxyethylcellulose.

A high viscosity for the processing agent is very desirable since itmakes possible the relatively uniform spreading of the composition andinsuresa complete coverage of the desired area by said composition. Thefilm-forming material is preferably contained in the composition insuitable quantities to impart to the composition a vis cosity in excessof 1,000 centipoises at a temperature of approximately 24 C. andpreferably of the order of 1,000 to 200,000 centipoises at saidtemperature.

Examples of developers useful in the foregoing composition alone or inmixture with one another are hydroquinone, monomethyl-p-aminophenolsulfate, p-aminophenol hydrochloride, p-hydroxyphenylaminoacetic acid,p-phenylenediamine, o-phenylenediamine, pyrocatechin (pyrocatechol,catechol), diaminophenol dihydrochloride, diaminophenol hydrochloride,pyrogallol, chlorohydroquinone, dichlorohydroquinone,tetrachlorohydroquinone, bromohydroquinone, toluhydroquinone,xylohydroquinone, o-aminophenol, Z-amino-S-diethylaminotoluenehydrochloride, p-tertiary butyl catec-hol, hydroquinone disulfonic acid(potassium salt), 2,5-ditertiary butyl hydroquinone, andp-aminodiethylaniline.

Examples of materials which may be used in the composition for thepurpose of forming a soluble silver complex with the undeveloped silverhalide of the photosensitive layer are sodium thiosulfate, sodiumthiocyanate, ammonium thiosulfate, ammonia and sodium cyanide. When acompound is toxic, such as sodium cyanide, precautions should be takenin the use thereof.

The composition may also contain sodium sulfite which acts in part as apreservative, and may also function as a silver halide solvent.

Referring now to FIGURE 1, one embodiment of the novel photosensitiveemulsion layers of the present invention in the performance of atransfer process for the production of positive silver prints comprisesa spreader sheet 10, a layer of relatively viscous processing agent 11,a photosensitive emulsion layer 12 comprising the specified hydroxyethylpolyvinyl alcohol, an image-receiving layer 13 preferably containingsilver precipitating nuclei, such as the silver precipitating nuclei,disclosed in the aforementioned US. Patent No. 2,698,237, and a suitablesupport layer 14. Support layer 14 may comprise an opaque material wherea reflection print is desired or may comprise a transparent materialwhere a transparency is desired.

Liquid layer 11 may be obtained by spreading a photographic processingcomposition, for example, in a manner disclosed in US. Patent No.2,698,244, issued December 28, 1954. As disclosed in the aforementionedUS. patent, the liquid processing composition may be disposed in arupturable container so positioned with regard to the appropriatesurface of the photosensitive emulsion that, upon compression byspreader sheet 10, a substantially uniform layer 11 of processingcomposition is distributed over the surface of photosensitive emulsion12,

positioned distally from image-receiving layer 15. The processingcomposition may be one of the film-forming processing compositionsdisclosed in US. Patent No. 2,543,181, issued February 27, 1951. It maycomprise, for example, a developing agent such as hydroquinone, analkali such as sodium hydroxide, a silver halide complexing agent suchas sodium thiosulfate, and a high molecular weight film-formingthickening agent such as sodium carboxymethyl cellulose. All thesematerials are preferably in aqueous solution. The photographic agentsare preferably contained in solution in the processing liquid prior tothe spreadingthereof as layer 11, but they may be in part or in wholeadded to the processing composition as it is spread between spreadersheet 11 and photosensitive silver halide emulsion 12, said agents beingso located on or adjacent to the surface of one or both of said layersas to be dissolved by or otherwise interacted with the liquid agent whenthe latter wets said surface.

In carrying out the aforementioned transfer process, photosensitiveemulsion 12 is exposed to a predetermined subject matter to form thereina latent image of said subject matter. A substantially uniformdistribution of processing composition 11 is disposed on the externalsurface of said emulsion, for example, according to the previouslydescribed procedure. Processing composition reagents permeate into thephotosensitive emulsion, developing the latent image contained thereinaccording to the pint-t0-point degree of exposure thereof. Substantialiycontemporaneous with development of the latent image, an image-Wisedistribution of soluble silver complex is formed from undeveloped silverhalide within said emulsion. At least part of this silver complex,solubilized,

is transferred, by imbibition, to image-receiving stratum 13. Thetransferred silver complex is reacted to provide a positive, reversedimage of the latent image. Subsequent to formation of the positive imagein image-receiving layer 13, dissociation: of this layer from theemulsion layer 12 may be effected.

Where desired, the image-receiving layer 13 may be dissociated fromemulsion layer 12 by stripping the emulsion from the surface thereof. Aconventional stripping layer may be provided to facilitate separation ofemulsion layer 12 from image-receiving layer 13 subsequent tosubstantial transfer image formation. The stripping layer may be coatedon the surface of the image-receiving element and the photosensitiveemulsion thereafter coated on the external surface of the strippinglayer. Suificient abrasion-resistant properties may be provided toimagereceiving element 13 such as to obviate any nemssity ofsubsequently over-coating to prevent subsequent laceration and resultantdegradation of the transfer image.

In the aforementioned processes, spreading of the liquid processingcomposition on the external surface of the photosensitive emulsion ispreferably effected by rupture of a suitably positioned frangiblecontainer and distribution of its processing composition content bymeans of a spreader sheet such as converted cellulose acetate; that is,a cellulose acetate sheet, the surface of which has been converted tocellulose. A spreader sheet may be chosen which exhibits an adhesivecapacity for the processing composition in excess of the adhesivecapacity exhibited by the hydroxyethyl polyvinyl alcohol containingphotosensitive emulsion. A means is thus provided for effectingdissociation of the processing composition from contact with thephotosensitive emulsion, preferably subsequent to image formation,dissociating the spreader sheet from proximate relationship to theexternal emulsion surface.

A further embodiment of the present invention is illustrated in FIG. 2,which comprises a photosensitive hydroxyethyl polyvinyl alcohol emulsion12, a layer of the previously-noted, relatively viscous, film-formingprocessing composition, and an image-receiving layer 15, preferablycontaining silver precipitating nuclei.

As previously stated, layer 11 of processing composition may bedistributed in a substantially uniform manner, between photosensitiveemulsion layer 12 and imagereceiving layer 15, for example, inaccordance with the procedures disclosed in the aforementioned US.Patent No. 2,543,181. For example, one or more rupturable containers maybe attached to either photosensitive emulsion layer 12 and/ orimage-receiving layer 15 such that upon superposition of the respectivelayers 12 and 15 the container of containers are so positioned as to becapable, upon rupture, of releasing their contents in a substantiallyuniform layer between and in contact with the opposed surface of each ofsaid layers. Rupture of the container or containers and spreading of thecontents thereof may be accomplished, for example, by compressionbetween a pair of opposed, suitably gapped rollers.

In carrying out the aforementioned transfer process, the photosensitiveemulsion 12 is exposed to a predetermined subject matter to form thereina latent image of said subject matter. The exposed emulsion issuperposed on image-receiving layer 1d and the photographic processingcomposition 11 spread between the opposed surfaces of photosensitiveemulsion 12 and image-receiving layer 15. Reagents permeate into thephotosensitive emulsion 12, developing the latent image containedtherein and forming a soluble silver complex of undeveloped silverhalide. Soluble silver complex is then transported from photosensitiveemulsion layer 12, at least in part, by imbibition, to image-receivingstratum 15 and the silver of the complex there precipitated to providethe desired transfer image formation. The lamination formed bythespreading of processing composition in layer 11, between photosensitiveemulsion 12 and image-receiving layerld, is kept intact for less than 90seconds, preferably about 10 seconds or less, and at the termination ofthis time interval, image-receiving layer 15 is dissociated fromemulsion 12, as for example, by stripping.

As illustrated in FIG. 3, one embodiment of the present invention, foruse in additive multicolor diffusion transfer processes, is a compositefilm unit comprising a transparent support 16, an additive color screenelement 17, an image-receiving layer 13 preferably containing silverprecipitating nuclei, and a hydroxyethyl polyvinyl alcohol containingphotosensitive emulsion 12.

In carrying out an additive multicolor diffusion transfer processutilizing the aforementioned composite film unit, exposure of thephotosensitive emulsion to a predetermined subject matter is eifectedthrough color screen element 17. A liquid processing composition isapplied to photosensitive emulsion 12, as for example, according to theprocedure previously described in explanation of FIG- URE 1. The liquidprocessing composition permeates into photosensitive emulsion 12,developing the latent image contained therein, forming an image-wisedistribution of soluble silver complex in undeveloped areas thereof, andtransferring, at least part of said image-wise distribution, byimbibition, toward image-receiving layer 13, wherein the silver of saidcomplex is precipitated to provide positive silver image formation.Dissociation of emulsion layer 12 from image-receiving layer 13 may beaccomplished, for example, according to the procedure previouslydescribed in explanation of FEGURE 1. As previously stated, in additivemulticolor processes the viewing of the positive image takes placethrough a permanently registered color screen element, either that colorscreen element through which exposure was accomplished or a duplicatethereof. Although, in the aforernentioned process, exposure isaccomplished through the stationary color screen element predisposed inthe imagereceiving element, thus avoiding the problem incident uponattempts to register a mobile color screen element with the depositedsilver image, it must be noted that the instant inventive concepts areequally applicable to the numerous additive multicolor diffusiontransfer processes utilizing color screen elements in combination withsilver transfer processes, such as, for example, the additive multicolortransfer processes disclosed in U.S. Patent No. 2,614,926, issuedOctober 21, 1952.

U.S. Patent No. 2,707,150, issued April 26, 1955, discloses additivemulticolor processes utilizing a color screen element in aphotosensitive emulsion wherein, subsequent to the selective exposure ofthe photosensitive emulsion through said color screen and substantiallysimultaneous with the development of the latent image contained therein,the color screen element filter media, preferably soluble dyes,transfer, at least in part, by diffusion to an image-receiving elementto provide thereto a substantially duplicate screen element of theoriginal color screen element.

In the following description of FIG. 4, the term imageforming componentis intended to signify the image-dye precursors utilized in thepreviously noted color coupling and dye developer diffusion transfertechniques, as well as the coupling dye techniques disclosed in U.S.Patent No. 2,774,668, issued December 18, 1956, and the copending U.S.application of Howard G. Rogers, Serial No. 613,691, filed October 3,1956, to provide monochromatic and/ or multichromatic subtractive colorimage formation.

FIG. 4 of the accompanying drawing illustrates one method of processinga photosensitive element to obtain a subtractive color transfer image inaccordance with this invention. A photosensitive element 19 comprises asup- .port 14, a layer 18 containing at least one color imageformingcomponent, preferably at least one dye developer, and a photosensitivehydroxyethyl polyvinyl alcohol containing emulsion layer 12. As shown inthe particular embodiment depicted in FIG. 4, the photosensitive elementis shown in a spread apart relationship (as, for example, duringexposure) with an image-receiving layer 15 having mounted thereon arupturable container 20 holding a processing composition. Afterexposure, imagereceiving element 15 is brought into superposedrelationship with the photosensitive element 19 and the rupturablecontainer 20 is ruptured by application of suitable pressure, forexample, by advancing between a pair of rollers (not shown), and a layerof the liquid processing composition permeates the photosensitiveemulsion layer 12 and layer 18 containing image-forming componentsproviding at least subtractive image color. In exposed areas of thephotosensitive element, the image-forming components, at least to someextent, exhibit decreased solubility in contradistinction to unexposedareas. Thus, in unexposed areas the image-forming components willtransfer, at least in part, by diffusion, to superposed image-receivingelement 15 to provide thereto a positive image in terms of saidunexposed areas. Image-receiving element 15 may then be separated fromsuperposed relationship with the photosensitive element after at least aportion of the image-forming components have been transferred.

It is also contemplated to utilize, in the preparation of substractivecolor images, a film structure similar to FIGURE 1, wherein thephotosensitive hydroxyethyl polyvinyl alcohol emulsion is coated overthe image-receiving element and the processing composition must permeatethrough the emulsion before reaching the image-receiving layer.

Multicolor images may be obtained using image-forming components anddiffusion transfer processes by several techniques. One such techniquecontemplates the use of a photosensitive stratum comprising at least twosets of selectively sensitized, minute, photosensitive elements arrangedin the form of a photosensitive screen. Transfer processes of this typeare disclosed in the aforementioned U.S. Patent No. 2,938,606. In suchan embodiment, each of the minute photosensitive elements I hasassociated therewith appropriate color image-forming components in orbehind the photosensitive emulsion portion. In general, a suitablephotosensitive screen, prepared in accordance with the disclosure of thelastmentioned patent, comprises minute red-sensitive emulsion elements,minute green-sensitive emulsion elements and minute blue-sensitiveemulsion elements arranged in a side-by-side relationship in a screenpattern and which have associated therewith, respectively, cyan colorimageforming components.

Another process for obtaining multicolor transfer images utilizingimage-forming components employs an integral multi-layer photosensitiveelement wherein at least two selectively sensitized photosensitivestrata are superposed on a single support and are processed,simultaneously, and without separation, with a single, commonimage-receiving layer. A suitable arrangement of this type comprises asupport carrying a red-sensitive emulsion stratum, a green-sensitiveemulsion stratum and a bluesensitive emulsion stratum, said emulsionshaving associated therewith, respectively, cyan image-formingcomponents, magenta image-forming components and yellow image-formingcomponents. The color image-forming component may be disposed in theemulsion layer, for example, in the form of particles, or one or moremay be employed, respectively, as a layer behind the appropriatephotosensitive emulsion strata. Each set of emulsions and associatedcolor image-forming components may be separated from other sets bysuitable interlayers, for example, by a layer or layers of gelatin orpolyvinyl alcohol.

A further technique for obtaining multicolor image employs a pluralityof photosensitive elements associated with appropriate numbers ofimage-receiving elements .and adapted to be treated with one or moreliquid processing compositions, the appropriate color image-formingcomponents being incorporated in the respective photosensitive elements.Examples of film structures of this type are disclosed in aforementionedU.S. Patent No. 2,647,049.

While a rupturable container, such as container 20 in FIG.4, provides aconvenient means for spreading a liquid processing composition betweenlayers of a film unit whereby to permit the processing to be effectedwithin a suitable camera apparatus, the processing of this invention maybe otherwise effected. For example, a photosensitive element, afterexposure in a suitable apparatus and while preventing further exposurethereafter to actinic light, may be removed from such apparatus andpermeated with the liquid processing composition, as by coating thecomposition on said photosensitive element or otherwise wetting saidelement with the composition, following which the permeated, exposed,photosensitive element, still without additional exposure to actiniclight, is brought into contact with the image-receiving element forimage formation in the manner heretofore described. Details of suchrupturable containers as are illustrated in FIG. 4, may be found in U.S.Patent No. 2,634,886, issued April 14, 1953.

The concepts of the present invention find equal applicability indiffusion transfer processes of the type disclosed in U.S. Patent No.2,846,309, issued August 5, 1958. In such processes, a fluidphotosensitive emulsion is coated on the opposed surface of a firstsupport element which is in superposed relationship to a second sheetimage-receiving element, photoexposed and processed with a transferprocessing composition to provide a transferimage to said second sheetelement.

Where desired, theinventive concepts of the present invention may beemployed in the spontaneous development transfer process disclosed andclaimed in the copending U.S. application of Edwin H. Land, Serial No.498,672, filed April 1, 1955. In such processes a transfer processingcomposition is contacted with a photosensitive emulsion which is insuperposed relationship to an image The term photosensitive" and otherterms of similar import are herein employed in the generic sense todescribe materials possessing physical and chemical properties whichenable them to form usable images when photoexposed by radiation.

Since certain changes may be made in the above products and processeswithout departing from the scope of the invention herein involved, it isintended that all matter contained in the above description or shown inthe accompanying drawing shall be interpreted as illustrative and not ina limiting sense.

What is claimed is:

1. In a diffusion transfer process which comprises the steps ofdeveloping an exposed photosensitive emulsion and forming thereby animage-wise distribution of imageforrning components in saidphotosensitive emulsion, as a function of the point-to-point degree ofexposure thereof, and transferring, at least part of said image-wisedistribution, by diffusion, to a contiguous image-receiving layer toprovide thereto a visible transfer image, the improvement whichcomprises employing a hydroxyethyl polyvinyl alcohol silver halidephotosensitive emulsion.

References Cited by the Examiner UNITED STATES PATENTS 2,687,478 8/54Land 96-76 3,017,270 1/62 Tregillus 96-29 3,043,691 7/62 Weyde 96-293,043,698 7/62 Chambers 96-114 3,061,428 10/62 Haas 96-290 3,077,4002/63 Rogers et al. 96-3 3,108,001 10/63 Green 96-29 OTHER REFERENCESCohen et al.: J. Poly. Sci., 11, 193-201 (1953).

NORMAN G. TORCHIN, Primary Examiner.

1. IN A DIFFUSION TRANSFER PROCESS WHICH COMPRISES THE STEPS OF DEVELOPING AN EXPOSED PHOTOSENSITIVE EMULSION AND FORMING THEREBY AN IMAGE-WISE DISTRIBUTION OF IMAGEFORMING COMPONENTS IN SAID PHOTOSENSITIVE EMULSION, AS A FUNCTION OF THE POINT-TO-POINT DEGREE OF EXPOSURE, THEREOF, AND TRANSFERRING, AT LEAST PART OF SAID IMAGE-WISE DISTRIBUTION, BY DIFFUSION, TO A CONTIGUOUS IMAGE-RECEIVING LAYER TO PROVIDE THERETO A VISIBLE TRANSFER IMAGE, THE IMPROVEMENT WHICH COMPRISES EMPLOYING A HYDROXYETHYL POLYVINYL ALCOHOL SILVER HALIDE PHOTOSENSITIVE EMULSION. 